. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. ORCHIDEAE 407 like a helmet, directed upwards, and secretes nectar on its inner side. The five other downwardly directed perianth leaves are long, narrow, and slightly bent upwards, thus enclosing a space, in the middle of which the column consisting of stigma and anther is situated; this slopes gently upwards and forms an alighting- platform. Kemer states that humble-bees probing for nectar touch this platform with the under-side of their bodies in climbing
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. ORCHIDEAE 407 like a helmet, directed upwards, and secretes nectar on its inner side. The five other downwardly directed perianth leaves are long, narrow, and slightly bent upwards, thus enclosing a space, in the middle of which the column consisting of stigma and anther is situated; this slopes gently upwards and forms an alighting- platform. Kemer states that humble-bees probing for nectar touch this platform with the under-side of their bodies in climbing upwards over it. On the downwardly directed end of the column are situated first the anther, next the rostellum, with very sticky papillae, and finally, still higher up, the stigma, forming a steep wall. The ovoid pollinia are united to the sticky papillae of the rostellum by long, tough threads, and covered by a membranous cap belonging to the anther. The wood humble-bee (Bombus lucorum Z.) found in shady woods, uses the column as an alighting - platform, and from its lower edge probes for nectar in the galeate labellum; it does not immediately come into contact with the concealed pollinia, but the sticky papillae of the rostellum adhere to the under-side of its body. When the insect leaves the flower, the cap covering the pol- linia springs back, so that the two pollinia clinging to the disks are torn out and carried away. At the same time they turn over, so that they now hang downwards from their caudicles like two cherries on their stalks. The whole of the structure thus torn out elongates somewhat, so that the pollinia can be deposited on the stigma of another flower. The stigma is situated above the rostellum, and if the pollinia did not possess long caudicles, they could not be pressed on it by humble-bee visitors. Rohrbach, who has described the flower-mechanism very minutely, states that the spur and the upper margin of the labellum serve as an alighting-platform for
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